1. Field of the Invention
The present invention relates to a conductive roller for use in an image-forming apparatus such as an electrophotographic copying machine or a printer, and to a method for inspecting the roller. More particularly, the invention relates to a conductive roller suitable for a development roller and to an inspection method therefor.
2. Background Art
Conventionally, a development roller for use in an image-forming apparatus is formed of a polyurethane material to which an ion-conducting agent such as lithium perchlorate has been added.
Such a development roller containing an ion-conducting agent has a drawback in that electric resistance of the roller varies considerably in accordance with variation in use conditions. Specifically, under low temperature and low humidity conditions, resistance value increases, resulting in insufficient charging of a toner, and under high temperature and high humidity conditions, resistance value decreases, resulting in fogging of a toner, Needless to say, both cases result in image failure.
Meanwhile, there has been investigated a development roller to which electrical conductivity has been imparted by use of carbon black. Such a development roller exhibits comparatively small environmental dependency, but large charge in electrical resistance in accordance with applied voltage, which is problematic. In addition, variation in electric resistance value makes it difficult to control electrical resistance to a predetermined value, which is also problematic.
Under the foregoing circumstances, a development roller which can be used with consistent performance was previously proposed. Specifically, Japanese Patent Laid-Open (kokai) No. 2003-202750 (in claims and other sections) discloses the development roller to which electrical conductivity has been imparted by use of carbon black, in which variation in electrical resistance is minimized to obtain a predetermined resistance value.
However, the present inventors have found that image quality of actually obtained printed products cannot be predicted on the sole basis of variation in electrical resistance. In other words, even under the same variation conditions in electrical resistance, quality of obtained images may vary.